The present invention relates generally to automotive finishes, and more particularly, to methods of manufacturing automotive finishes of the thermosetting type.
Presently, at least one major automobile manufacturer in this country is using a thermosetting arcylic resin solution to paint its cars. This thermosetting acrylic solution is known to the art as "NAD Type II". Although this NAD Type II thermosetting acrylic resin is compatible with many other standard dispersant resins, upon extended exposure tests, where the resultant auto finishes are exposed to the sun over a period of approximately two years, the resultant auto finish lacks durability and may exhibit either a dullness or a slight separation of pigment and resin, i.e. a loss of finish uniformity which is considered to be unacceptable in most auto finishes. Accordingly, it is common practice to avoid any dispersion of pigments in any other resin other than NAD Type II. Therefore, according to the present techniques, NAD Type II is dispersed at an automotive plant in a ball mill with the desired pigment in order to produce a sprayable resin composition having approximately ten percent (10%) pigment loading. In this ball mill operation, the ball mill itself is utilized to grind the pigment and to disperse the pigment in the final NAD Type II thermosetting acrylic resin solution. Attempts at predispersing pigments in NAD Type II resins have not been economically practical since NAD Type II may be loaded with pigment only to approximately twenty weight percent, at which percentage a sprayable viscosity is not present. NAD Type II resin is a liquid in its natural state and is therefore difficult to handle, minimizing the practicality of predispersing pigment (or other resin additives) therein prior to use. Half as much predispersed resin additive must be prepared and shipped by the dispersion house as is required for the final end use, thereby giving rise to the present practice of initially preparing final dispersions as paint is required.
In addition to the above problems, any predispersed resin additive must be suitable for use with the various ketone and aromatic solvents which are commonly added to NAD Type II resin systems for the purpose of controlling the viscosity and drying time. An otherwise suitable predispersed composition will not be acceptable to the industry if such a ketone-aromatic solvent compatability is not evidenced.
Although NAD Type II thermosetting acrylic automotive finishes have met with some success, it is nonetheless necessary for the particular automotive manufacturers to make substantial investments in ball mills installed at or near the paint site which must run for between 24 and 72 hours, during which time the pigment is ground and dispersed into the NAD Type II-type acrylic resin solution.